Funds are requested for the purchase of instrumentation about with we may establish a "core" facility for quantitative electron microprobe analysis. Seven major projects will utilize this facility; five of these will depend on the use of cryosectioned soft tissues where frozen-dried sections will be assessed for intracellular electrolyte composition by energy-dispersive x-ray analysis; one of these projects and two others will primarily depend on analysis of picoliter liquid samples of biologically derived fluids. The projects include investigations of: 1) subcellular solute distribution during vasopressin-induced osmotic water flow across the toad urinary bladder epithelium, 2) regulation of transport activity in high resistance amphibian epithelia by aldosterone, metabolism and intracellular pH, 3) epithelial secretory mechanisms in the mammalian intestine, 4) the role of cytoplasmic electrolytes in renal tubuloglomerular feedback responses, 5) elemental composition of fluid absorbed by isolated, perfused segments of the rabbit nephron, 6) ionic involvement in stimulus-secretion coupling in the pancreatic Beta-cell, and 7) the regulation of transport in the loop of Henle of the rat. The hardware we project for these tasks consists of a scanning electron microscope equipped with a computer controlled energy-dispersive x-ray microanalysis system and a cryoultramicrotome. Necessary ancillary equipment includes a sputter-coater, a freeze-drying unit, a glass knife maker, a stereo dissection microscope and an atomic absorption spectrometer. Custom modifications to requested equipment are minimal and will follow along lines previously established at a comparable facility where their design has proven effective.